1. Field of the Invention
The present invention relates computer graphics chips.
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2. Background Art
Computer systems are often used to generate and display graphics on an output device such as a monitor. When complex and realistic graphics are desired there are often additional components, or chips, that are added to the computer system to assist it with the complex instruction processing that it must perform to render the graphics to the screen. Graphics chips may be considered as having a front-end and a back-end. The front-end typically receives graphics instructions and generates “primitives” that form the basis for the back-end's work. The back-end receives the primitives and performs the operations necessary to send the data to a frame buffer where it will eventually be rendered to the screen. As will be further described below, graphics chip back-ends are currently inadequate. Before further discussing this problem, an overview of a graphics system is provided.
Graphics System
Display images are made up of thousands of tiny dots, where each dot is one of thousands or millions of colors. These dots are known as picture elements, or “pixels”. Each pixel has multiple attributes associated with it, including a color and a texture which is represented by a number value stored in the computer system. A three dimensional display image, although displayed using a two dimensional array of pixels, may in fact be created by rendering of a plurality of graphical objects. Examples of graphical objects include points, lines, polygons, and three dimensional solid objects. Points, lines, and polygons represent rendering primitives which are the basis for most rendering instructions. More complex structures, such as three dimensional objects, are formed from a combination or mesh of such primitives. To display a particular scene, the visible primitives associated with the scene are drawn individually by determining those pixels that fall within the edges of the primitive, and obtaining the attributes of the primitive that correspond to each of those pixels. The obtained attributes are used to determine the displayed color values of applicable pixels.
Sometimes, a three dimensional display image is formed from overlapping primitives or surfaces. A blending function based on an opacity value associated with each pixel of each primitive is used to blend the colors of overlapping surfaces or layers when the top surface is not completely opaque. The final displayed color of an individual pixel may thus be a blend of colors from multiple surfaces or layers.
In some cases, graphical data is rendered by executing instructions from an application that is drawing data to a display. During image rendering, three dimensional data is processed into a two dimensional image suitable for display. The three dimensional image data represents attributes such as color, opacity, texture, depth, and perspective information. The draw commands from a program drawing to the display may include, for example, X and Y coordinates for the vertices of the primitive, as well as some attribute parameters for the primitive (color and depth or “Z” data), and a drawing command. The execution of drawing commands to generate a display image is known as graphics processing.
Graphics Processing Chips
When complex graphics processing is required, such as using primitives to as a basis for rendering instructions or texturing geometric patterns, graphics chips are added to the computer system. Graphics chips are specifically designed to handle the complex and tedious instruction processing that must be used to render the graphics to the screen. Graphics chips have a front-end and a back-end. The front-end typically receives graphics instructions and generates the primitives or combination of primitives that define geometric patterns.
The primitives are then processed by the back end where they might be textured, shaded, colored, or otherwise prepared for final output. When the primitives have been fully processed by the back end, the pixels on the screen will each have a specific number value that defines a unique color attribute the pixel will have when it is drawn. This final value is sent to a frame buffer in the back-end, where the value is used at the appropriate time.
Modern graphics processing chip back-ends are equipped to handle three-dimensional data, since three-dimensional data produces more realistic results to the screen. When processing three-dimensional data, memory bandwidth becomes a limitation on performance. The progression of graphics processing back-ends has been from a 32 bit system, to a 64 bit system, and to a 128 bit system. Moving to a 256 bit system, where 512 bits may be processed in a single logic clock cycle, presents problems. In particular, the efficient organization and use of data “words” with a 256 bit wide DDR frame buffer is problematic because the granularity is too coarse. Increasing the width of the frame buffer to 256 bits requires innovations in the input and output (I/O) system used by the graphics processing back-end.